Anti-backlash nuts, per se, are commercially available today in many forms and sizes. One of their important uses is to drive an element of a machine in a linear path with accurate positional repeatability and constant drag torque control in both the forward and reverse directions. For example, data printers and XY tables, used as peripheral equipment in the computer industry, have such requirements. Generally speaking, the anti-backlash nut is a nonrotatable member physically attached to a machine element. It is driven linearly in both forward and reverse directions by the rotation of a lead screw to which it is threadably attached. Such anti-backlash mechanisms will be found in our earlier U.S. Pat. Nos. 4,131,031, 4,249,426 and RE 32,433. We have found that such mechanisms are ideal for the creation of anti-backlash linear motion, not of the nut, per se, but of the lead screw which heretofore drove the nut.
There are numerous requirements today for very accurate linear reciprocation, as for example, a piston of pumping mechanism for chemical or medical analysis apparatus. Accuracy is also required in raising and lowering of apparatus in a predictable and repeatable sequence in robotic applications.
One example of a motorized anti-backlash linear actuator is disclosed in the present inventors' U.S. Pat. No. 4,974,464. This patent describes an actuator having a motor in a casing and an anti-backlash nut extending out from the motor casing. In such a device, the motorized components can result in large temperature disparities between operating and non-operating conditions, which can have unpredictable consequences on the various components of the device, particularly if they have different thermal properties. Also, the fact that the anti-backlash nut extends a significant distance outside of the motor casing can make the device unstable, particularly when the anti-backlash nut is rotated at high speeds.